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libvirt: Log breadcrumb for known encryption bug

The initial implementation of native LUKS support within Libvirt
introduced a small issue when using a passphrase that is a multiple of
16 bytes in size. This is documented in the following bug and associated
patch posted to the Libvirt development list:

Unable to use LUKS passphrase that is exactly 16 bytes long

[libvirt] [PATCH] Fix padding of encrypted data

This change introduces a known issue release note and logs an additional
breadcrumb when we appear to hit this with pointers to the above.

Closes-Bug: #1778044
Change-Id: Id346bce6e47431988cce7001abcf29a9faf2936a
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lyarwood committed Jun 20, 2018
1 parent afcf078 commit 78891c2305bff6e16706339a9c5eca99a84e409c
@@ -7434,6 +7434,46 @@ def test_check_discard_for_attach_volume_blk_controller_no_unmap(self,
self._test_check_discard(mock_log, driver_discard=None,
bus='virtio', should_log=False)

def test_attach_volume_with_libvirt_bug_breadcrumb(self, mock_get_info):
drvr = libvirt_driver.LibvirtDriver(fake.FakeVirtAPI(), False)
instance = objects.Instance(**self.test_instance)
connection_info = {"driver_volume_type": "fake",
"data": {"device_path": "/fake",
"access_mode": "rw"}}
bdm = {'device_name': 'vdb',
'disk_bus': 'fake-bus',
'device_type': 'fake-type'}
disk_info = {'bus': bdm['disk_bus'], 'type': bdm['device_type'],
'dev': 'vdb'}
libvirt_exc = fakelibvirt.make_libvirtError(fakelibvirt.libvirtError,
"unable to execute QEMU command 'object-add': Incorrect number"
" of padding bytes (56) found on decrypted data",

with test.nested(
mock.patch.object(drvr._host, 'get_guest'),
mock.patch.object(drvr, '_connect_volume'),
mock.patch.object(drvr, '_get_volume_config'),
mock.patch.object(drvr, '_check_discard_for_attach_volume'),
mock.patch.object(drvr, '_build_device_metadata'),
) as (mock_get_guest, mock_log, mock_connect_volume,
mock_get_volume_config, mock_check_discard, mock_build_metadata):

mock_conf = mock.MagicMock()
mock_guest = mock.MagicMock()
mock_guest.attach_device.side_effect = libvirt_exc
mock_get_volume_config.return_value = mock_conf
mock_get_guest.return_value = mock_guest
mock_get_info.return_value = disk_info
mock_build_metadata.return_value = objects.InstanceDeviceMetadata()

self.assertRaises(fakelibvirt.libvirtError, drvr.attach_volume,
self.context, connection_info, instance, "/dev/vdb",
disk_bus=bdm['disk_bus'], device_type=bdm['device_type'])

@@ -1415,6 +1415,16 @@ def attach_volume(self, context, connection_info, instance, mountpoint,
instance.device_metadata = self._build_device_metadata(
context, instance)

# TODO(lyarwood) Remove the following breadcrumb once all supported
# distributions provide Libvirt 3.3.0 or earlier with
#;a=commit;h=7189099 applied.
except libvirt.libvirtError as ex:
if 'Incorrect number of padding bytes' in six.text_type(ex):
LOG.warning(_('Failed to attach encrypted volume due to a '
'known Libvirt issue, see the following bug for details: '
except Exception:
LOG.exception(_('Failed to attach volume at mountpoint: %s'),
mountpoint, instance=instance)
@@ -0,0 +1,15 @@
- |
The initial implementation of native LUKS decryption within Libvirt 2.2.0
had a `known issue`_ with the use of passphrases that were a multiple of 16
bytes in size. This was `resolved`_ in the upstream 3.3.0 release of
Libvirt and has been backported to various downstream distribution specific
A simple warning will reference the above if this issue is encountered by
Nova however operators of the environment will still need to update
Libvirt to a version where this issue has been fixed to resolve the issue.
.. _known issue:
.. _resolved:;a=commit;h=7189099

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